Laser welding system

ABSTRACT

The present invention relates generally to an improved laser welded work piece, such as an automotive body panel, and a system and method for the manufacture thereof. The invention is also directed to an improved system for manufacturing the welded work piece including an improved laser welder and a laser weld inspection device and system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/262,248, filed Mar. 4, 1999 Now U.S. Pat. No. 6,204,469, entitled“Laser Welding System.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a new automated laser weldingsystem configured to produce, for example, an improved welded workpiece, such as an automotive body panel, and a system and method for themanufacture thereof that includes an improved laser welder and a visualweld inspection device. The invention also relates to a method forperforming an automated quality control inspection of a laser weld.

2. Background

In the past, welded work pieces such as body panels for use in theautomotive vehicle industry were made by stamping or drawing the panelfrom either a single blank of a ductile sheet metal material, includingsteel, or from a plurality of such blanks that were previously weldedtogether. Either type of welded work piece or body panel usuallyrequired the addition of stiffeners and pads welded to sections of thepanel to improve its structural rigidity. The added stiffeners and padswere also needed to increase the thickness of the work piece inpredetermined locations so that various structural and fasteningassemblies could be fastened and welded to the panel without damageduring the fastening or welding process. The addition of the stiffenersand pads increased the weight of the work piece and also increased thetotal manufacturing time needed to fabricate the work piece. The workpieces were often formed, drawn, or stamped into a final shape to have athree-dimensional shape corresponding to the overall design of theautomotive vehicle.

As a result of the number of manufacturers in the field, the automotivevehicle industry is very competitive with respect to, among otherthings, quality, raw material costs, and manufacturing times required tocompletely fabricate and assemble a vehicle. To remain competitive,manufacturers have continuously expended enormous resources to contain,if not reduce, material costs by reducing part weight, part count, andmanufacturing time while maintaining the needed high degree of quality.A considerable amount of such resources have been directed to improvingand automating routine tasks such as the fastening together of variouswork pieces and vehicle parts such as, for example, body panels forfenders, quarter panels, trunk lids, engine compartment hoods, vehicledoors, and other various components.

Previously, multi-part sheet metal blanks have been welded together intoa single work piece before being stamped into a final shape. Theseblanks were prepared by a variety of fastening techniques includingchemical, arc, and CO₂ laser welding, riveting, bolting, cold forming,and similar methods. Of particular interest in recent years is the useof more efficient laser welding using CO₂ lasers in automated,numerically controlled manufacturing processes. Such laser welding canbe accomplished for joining together sheet metal blanks at a common seamby means of, for example, a lap weld, or a butt weld. Butt welds areoften preferred because only a single seam needs to be welded incontrast to lap joint which usually require that two seams be welded.

Many problems have been associated with the use of CO₂ lasers includingthe requirement that less than optimum welding speeds must be usedbecause of the poor absorption by steel work pieces of the energyproduced by the CO₂ laser. Also, laser welded joints can be plagued withproblems despite the use of an appropriate weld speed if a manufacturerdoes not carefully prepare the work pieces or is otherwise not attentiveto the intricacies and pitfalls of laser welding processes. Problems areeven more prevalent when the blanks to be welded together are ofdissimilar thickness. Such problems include, for example, mismatchbetween the welded parts along the joint on at least one exteriorsurface, poor weld bead dimensions or hardness, cracks, poor weld beadcontinuity across the length of the weld, and pinholes formed in theweld bead. Many of these welding problems are difficult to avoid andeven more difficult to detect. More often than not, detection of suchproblems can only be accomplished by a slow and tedious visualinspection. Further, some of these problems, such as cracks, weldspatter, and pinholes, can only be detected through destructive testingsuch as by tension and shear tests, micrographic cross-sectionalanalysis, etch and penetrant dye inspections, and formability testing toensure the welded blanks of the work piece can be drawn or stampedwithout failure anywhere along the welded joint.

These problems are especially apparent when steel work pieces, such aswelded components for an automotive body or door panel, are to be buttwelded together for form a larger, single work piece or door panel blankthat can be later stamped or drawn into a shaped panel ready forpainting and attachment to the vehicle. In many cases such welds arestraight line weldments that could be completed faster if an improvedlaser welding technique were available. Additionally, it would bedesirable to have an automated manufacturing assembly line whereinmultiple work pieces could be automatically introduced to the laserwelding apparatus to minimize the risk of injuries to workers fromreflected laser energy. Further, such welding manufacturing processescould be made more efficient if a technique existed to speed up thepost-weld inspection process.

There have been attempts to develop a viable method for laser weldinginspection. United States Patent No. 5,607,605 discloses such a method,which utilizes a CCD (Charge U.S. Pat. No. 5,607,605 discloses such amethod, which utilizes a CCD (Charge Coupled Device) camera to capturean image of the plasma generated when a laser beam contacts an object tobe welded. The image is then sent to an image processing device, whichmeasures a selected particular feature of the plasma cloud. Themeasurement is further transferred to a distinction device, whichcompares the measurement with a reference value to determine if thelaser welding condition, and thus the weld, is acceptable.

Electro-optical detection of laser welding conditions has also beenemployed as an inspection method. U.S. Pat. No. 5,272,312 recites amethod for the inspection of a laser weld, wherein the area of thematerial in contact with the laser beam, referred to as the laserprocessing spot, is projected onto at least one photodetector such asphotodiode which detects the amount of liquid material ejected from theweld pool during the welding process. The signal from the photodiode canbe converted into an electrical signal, which may then be sent to aprocessing unit for determination of the size and location of voids orpores in the weld seam. In one embodiment, this reference discloses thedetection of ultraviolet radiation present in the plasma cloud.

Laser welding generates particular signals which may be monitored todetermine the quality of a weld. U.S. Pat. No. 5,681,490 discloses thatsensors such as photodiodes, phototransistors, photo darlingtons,pyroelectric detectors, microphones, and infrared and thermal detectorscan be positioned to monitor various stages of the welding process. Suchsensors may be utilized to monitor light, sound, gas, smoke,temperature, etc. The signals generated by these sensors may then beanalyzed by a computer to predict the weld quality.

None of the prior art, however, discloses an apparatus or methodutilizing direct inspection of the weld bead to determine the quality ofa laser weld. The prior art methods generally depend upon the use ofunstable process indicators to ascertain the condition of the weld,often requiring the monitoring and analysis of a multitude of signals toreach a conclusion regarding weld quality.

The automotive industry is in need of a laser welded work piece thatcontains fewer parts, has an optimally minimized weight, and that isproduced through the use of an automated, laser welding manufacturingprocess. The welded work piece produced in accordance with the presentinvention, and the system and method for its manufacture, overcomes thedeficiencies of the presently known methods for automated laser weldingand inspection of welded work pieces.

SUMMARY OF THE INVENTION

In general, the present invention is directed to an improved laserwelded work piece and an automated laser welding and visual inspectionsystem and method configured to manufacture the work piece. The weldedwork piece incorporates a minimized gap that is designed to improve thestructural properties of the laser weld. The new automated manufacturingsystem includes a robotically automated production line configured toprepare blank work pieces for welding by precision shearing at least oneedge, and to precisely align the blanks and laser weld them togetherusing a single or dual cell, high-speed, high-power laser. Duringwelding, the laser weld is concurrently inspected by a visual inspectiondevice to determine whether the welded work piece should be accepted orrejected. The operator can continuously supply palletized raw materials,such as pallets or skids of sheet metal blanks, to the production linewithout stopping or interrupting the automated production line. Afterwelding, the system robotically sorts and re-palletizes the finished,welded work piece onto accepted work piece skids or onto rejected workpiece skids. The operator can remove the accepted and rejected workpieces from the production line without stopping or interrupting thecontinuously running line.

The Welded Work Piece

The invention includes a welded work piece for use in manufacturing anautomotive vehicle that incorporates a first blank of a steel sheetstock with a first thickness and having at least one first precisionsheared edge, and a second blank formed from a steel sheet stockmaterial of a second thickness having at least one second precisionsheared edge. The first and second precision sheared edges are producedin the respective first and second blanks to form a minimized gapbetween the edges before welding. The edges are laser welded using theapparatus disclosed herein, to form a beaded seam that permanently joinsthe respective first and second blanks. In a method for manufacturingthe improved welded work piece, first and second blanks of a sheet stocksteel are selected to be of similar or dissimilar respective thicknessand respective precision sheared edges. The edges are positioned on aflat welding surface and tightly compressed together in an abuttingrelationship to form a minimized gap between the edges. The edges arethen laser welded together to form a beaded seam that permanently joinsthe blanks together to form the welded work piece.

There is thus disclosed a welded work piece for use in manufacturing anautomotive vehicle, comprising first and second sheet metal blanks, eachformed with at least one precision sheared edge and having similar ordissimilar thickness. The blanks form a minimized gap when therespective at least one precision sheared edges are positioned in anabutting relationship A continuous wave laser butt welded seam fixedlyjoins the blanks together along at least one of the respective precisionsheared edges.

The System

Another aspect of the present invention is directed to a system formanufacturing a welded work piece. The system includes at least onearticulating arm feeder robot, configured to retrieve at least one sheetmetal blank from a plurality of such blanks, from at least one of aplurality of feeder skids containing palletized sheet metal blanks. Thearm is adapted to transport the individual blanks, one at a time, fromthe skid to a load position on a magnetic conveyor. Each of the blanksare formed with at least one joining edge. In applications where blanksof dissimilar thickness or other dimensions are used, the blanks mayeither be stacked alternately on a single skid, or a second articulatingarm feeder robot may be employed to retrieve a dissimilar blank from asecond plurality of such blanks that are palletized on a secondplurality of skids. The second robot arm operates cooperatively to feedthe second, dissimilar blank onto the magnetic conveyer.

The magnetic conveyor of the system is adapted to receive from thefeeder robot or robots at least two blanks. The conveyer is configuredwith blank locator devices adapted to precisely position them on thesubstantially flat conveyor bed. The blanks are proximallypre-positioned so each of the respective joining edges are substantiallyparallel. The magnetic conveyor is further configured to releasablyrestrain the positioned blanks into place and to move the blanks fromthe load position to a shear position.

The system also incorporates a precision shear device positioned aboutthe shearing position of the magnetic conveyer. The shear device isconfigured with at least one upper stamping die that cooperates with atleast one lower stamping platen to precisely shear at least one of therespective joining edges of each of the blanks. After shearing, theblanks are moved by the magnetic conveyer onto an idle station thattemporarily stores the sheared blanks until they can be welded. Theblanks are then conveyed by a second conveyer to a welding gantrylocated at the other end of the idle station.

The second conveyer moves the sheared blanks onto a laser weld bed ofthe welding gantry. The gantry includes a clamping and positioningassembly operative to releasably register and press the respectivejoining edges of the blanks flat against the weld bed and tightlytogether with the edges in an abutting relationship to form a minimizedgap. The clamping mechanism is configured with a clamp assembly havingmultiple bars that clamp down on each blank to firmly press them againstthe laser weld bed. The positioning assembly includes a plurality oflocator assemblies that push against one or more of the non-joiningedges of each blank to precisely locate the blanks so that the precisionsheared edges are tightly pressed together. When so pressed together,the edges form a minimized gap or seam therebetween.

The system also includes a laser welder movably attached to the weldinggantry. The laser welder may be configured with a weld head powered by aremote laser power unit. The weld head moves along the gantry and, whenenergized, projects a laser beam incident to and focused upon the gap orseam of the blanks to form a weld bead seam. The system also comprises alaser weld inspection device that is adapted to move along either inconjunction with or independently of the laser weld head to inspect tothe weld bead seam. Once welded, an exit conveyor operates to remove thewelded work piece from the laser weld bed. An articulating arm exitrobot is also included that is configured to move the work piece fromthe exit conveyor to an exit station. If the inspection revealed thatthe weld was acceptable, the exit robot moves the welded work piece toone of a plurality of skids for work pieces that have passed theinspection. Otherwise, if the inspection revealed that the weld beadseam was not acceptable, the exit robot moves the defective welded workpiece to one of a possible plurality of reject skids.

There is thus disclosed a system for manufacturing a welded work piece,comprising at least one articulating arm feeder robot, configured toretrieve at least one blank from at least one of a plurality of feederskids of palletized sheet metal blanks. Each blank is formed with atleast one joining edge, and the articulating arm feeder robot is adaptedto transport the blank to a load position on a magnetic conveyor. Themagnetic conveyor is adapted to receive from the feeder robot or robotsat least two of the plurality of blanks and to precisely position themon a conveyor bed. The blanks are proximally pre-positioned so each ofthe respective joining edges are substantially parallel, and themagnetic conveyor is further configured to releasably restrain thepositioned blanks into place and to move them from the load position toa shear position. The system further comprises a precision shear device,positioned about the shearing position of the magnetic conveyer, andconfigured with at least one upper stamping die that cooperates with atleast one lower stamping platen to precisely shear at least one of therespective joining edges. There is also a welding gantry, spaced apartfrom the precision shear device and configured with a second conveyorhaving a laser weld bed and connected to the magnetic conveyer with anidle station therebetween. The second conveyer is configured to slidablyreceive the sheared blanks from the idle station and to move them ontothe laser weld bed. The system also utilizes a clamping and positioningassembly operative to releasably register and press the respectivejoining edges of the blanks flat against the weld bed and tightlytogether in an abutting relationship to form a minimized gap. A laserwelder is movably attached to the welding gantry, and has a weld headpowered by a remote laser power unit to project a laser beam incident toand focused upon the gap for welding the blanks along the gap to form aweld bead seam. A laser weld inspection device is slidably coupled tothe welding gantry and operative to inspect the weld bead. Afterinspection, an exit conveyor coupled to the second conveyor, removes thewelded work piece from the laser weld bed. An articulating arm exitrobot moves the work piece from the exit conveyor to an exit station,which is selected from the group of one of a plurality of accepted workpiece skids or a rejected work piece skid.

The system further includes a light curtain system that is configured tosurround each of the plurality of the feeder and exit station skids toallow removal and replacement of empty feeder and full exit skidswithout the need to interrupt the operating manufacturing system. If anoperator approaches any of the skids for removal and replacement, thelight curtains signal the robots either directly or indirectly. Inresponse, each of the robots is directed to another of the plurality ofskids for purposes of retrieving unwelded blanks or outputting weldedwork pieces during the period of time that the light curtain isactivated. Similarly, each of the skids or a skid holder unitincorporates a sensor that either signals that the skid is empty orfull. If either of these conditions occurs, the robot is directed to useanother of the plurality of skids.

There is further disclosed a method for manufacturing a welded workpiece comprising the steps of: shearing a precision edge on a respectivejoining edge of a plurality of sheet metal blanks, using a precisionshear device configured with at least one upper stamping die thatcooperates with at least one lower stamping platen to perform theshearing operation; moving the plurality of precision sheared blankstogether on a conveyor from the precision shear device to a laser weldbed of a welding gantry; precisely locating the blanks to register theprecision sheared edges in a compressed, abutting relationship; clampingthe respective joining edges of the blanks flat against the weld bed andtightly together in an abutting relationship to form a minimized gap;and laser welding the edges to form a beaded seam and to permanentlyjoin the blanks together.

The Laser Welder

In yet another aspect of the present invention, a single or multi-celledlaser welder is described. The laser welder incorporates at least onelaser weld head that is configured to movably project at least one laserbeam onto a plurality of work pieces to weld them together. As describedabove, the work pieces are positioned so that the edges are tightlypressed together in an abutting relationship to form a seam or gap. Thework pieces are welded together with a laser weld head that projects thelaser beam incident to the gap with a compound angle. The compound angleis measured relative to the vertical direction substantially normal tothe substantially flat sheet metal work pieces. A leading anglecomponent of the compound angle is substantially in the direction ofmovement of the laser weld beam as the weld head moves across the blanksduring welding. A leaning component of the compound angle is orthogonalto the leading angle and is substantially in the direction normal to theblanks and the gap and it leans to one side towards one of the blanksaway from the vertical direction.

Thus, there is disclosed a laser welder for welding a plurality of workpieces, comprising a laser weld head configured to movably project alaser beam onto a minimized gap formed between a plurality of adjacent,substantially flat work pieces formed with respective precision shearededges. The edges are positioned in an abutting relationship, and thelaser weld head is operative to weld the edges by forming a weld beadseam between the edges. The laser welder further comprises a laser beamincident on the gap with a compound angle. The compound angle ismeasured relative to the vertical direction substantially normal to thework pieces, and includes a leading angle component substantially in thedirection of movement of the laser weld beam, and a leaning componentsubstantially in the direction normal to the gap and leaning towards oneof the blanks away from the vertical direction.

There is further disclosed a multi-celled laser welder comprising aplurality of laser weld heads, each configured to movably project alaser beam onto a plurality of minimized gaps formed between a pluralityof adjacent, substantially flat work pieces formed with respectiveprecision sheared edges. The edges are positioned in an abuttingrelationship and the laser weld heads are operative to weld the edges byforming a weld bead seam between the edges. The laser beams are incidenton the gaps with a compound angle. The compound angle is measuredrelative to the vertical direction substantially normal to the workpieces, and includes a leading angle component substantially in thedirection of movement of the laser beams and a leaning componentsubstantially in the direction normal to the gaps and leaning towardsone of the blanks away from the vertical direction.

The Inspection System

The present invention is also directed to a specially designed visionsystem configured to inspect a laser weld bead in real time. When thefocal point of a laser beam contacts a work piece, it generates intenseheat which forms a molten weld pool. As the laser beam traverses thework piece, the weld pool left behind quickly cools to form a weld bead.A visual sensor, such as a CCD (Charge Coupled Device) or video camerafollows the laser welding head to view the weld bead. Although in apreferred embodiment of the invention a visual sensor is affixed to andtravels with the laser welding head, it should be realized that thevisual sensor could also be detached and independently propelled. Animage of the weld bead is captured by the visual sensor at apredetermined interval based on the velocity of the laser welding headand other factors. The image from the visual sensor is sent to an imageprocessing board, which in conjunction with a coprocessor board,computer and the system software, compare the image to a list ofpredefined, preferred tolerances, which correlate with severalestablished characteristics of the weld bead considered to beacceptable. If it is determined that the selected characteristics of theweld bead image are within the specified predefined tolerance limits, asignal is generated classifying the weld as acceptable. If it isdetermined that the image is outside the specified predefined tolerancelimits, a signal is generated classifying the weld as defective.

Thus, there is disclosed a laser welding inspection system comprising alaser welding device, an image capturing device for capturing the imageof a laser weld bead, and an image processing device in electroniccommunication with the image capturing device, for measuring at leastone dimension of the laser weld bead image captured by the imagecapturing device. The system further comprises a distinction device, inelectronic communication with the image processing device, for comparingthe value of the at least one dimension of the laser weld bead imagemeasured by the image processing device with a reference value, todetermine the quality of the laser weld.

There is further disclosed a method of inspecting a laser weld, themethod comprising capturing an image of a weld bead, measuring at leastone dimension of the laser weld bead image, and comparing the value ofthe dimension of the laser weld bead image with a reference value todetermine the quality of the laser weld.

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Without limiting the scope of the present invention as claimed below andreferring now to the drawings, wherein like reference numerals acrossthe various views refer to identical, corresponding, or equivalentfeatures and parts:

FIG. 1 is a planform view, in reduced scale, of a preferred embodimentof a welded work piece produced in accordance with the presentinvention;

FIG. 2 depicts a rotated, partial, cross-sectional view taken alongsection line 2—2 of FIG. 1, in enlarged scale, of the work piece of FIG.1 before welding;

FIG. 2a depicts a dimensional representation of an illustrative exampleof the work piece of FIG. 2;

FIG. 3 is a rotated, partial, cross-sectional view taken along sectionline 3—3 of FIG. 1, in enlarged scale, of the work piece of FIG. 1 afterwelding;

FIG. 3a is a schematic representation of another embodiment of the workpiece of FIG. 3;

FIG. 3b is a schematic representation of another embodiment of the workpiece of FIG. 3 wherein the lower surfaces of the welded work piece aremisaligned;

FIG. 4 is an elevated perspective view, in reduced scale, of a stampedbody panel fabricated from the welded work piece of FIG. 1;

FIG. 5 is schematic top-view, in reduced scale, of the layout of asystem for manufacturing the laser welded work piece of the presentinvention;

FIG. 6a is a schematic, rotated front-view taken along section line 6—6of FIG. 5, in enlarged scale, of a representative laser welder gantry, alaser welder, and a laser weld inspection device;

FIG. 6b is a detail view, in enlarged scale, of a portion of FIG. 6a andshowing the leading angle component of the compound angle of the laserbeam;

FIG. 6c is a section view taken along line 6 c-6 c of FIG. 6b andshowing the leaning angle component of the compound angle of the laserbeam;

FIG. 7 is a flow diagram representative of an exemplary embodiment ofthe comparison procedure used by the control computers or the laser weldinspection device, or both, of FIGS. 5, 6 a, and 6 b;

FIG. 8 is an enlarged view of a portion of FIG. 5 representing aplurality of the feeder skids, feeder robot arm, and light curtains ofthe manufacturing system of the present invention;

FIG. 9 is an enlarged view of a portion of FIG. 5 representing aplurality of the feeder skids, feeder robot arm, part of the magneticconveyor, and part of the precision shear machine of the manufacturingsystem of the present invention;

FIG. 10 is an enlarged view of a portion of FIG. 5 representing a secondconveyer, a weld gantry, a laser weld head, and work piece locators ofthe manufacturing system of the present invention; and

FIG. 11 is an enlarged view of a portion of FIG. 5 representing an exitconveyer, an exit robot arm, and a plurality of accepted work pieceskids and a rejected work piece skid of the manufacturing system of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention produces an improved welded work piece that is welded froma plurality of sheet metal blanks of substantially similar or dissimilarthickness, which are formed from materials such as steel, aluminum, andalloys. According to the invention, the plurality of blanks are laserwelded together at speeds faster than previously possible with a muchlower percentage of rejected work pieces. Before welding, the blanks areprecision sheared along at least one joining edge. The precision shearensures that when the sheared edges of the blanks are placed in anabutting relationship, a minimized gap, if any at all, will exist. Theclosely toleranced and minimized gap improves the final weldment andreduces the time needed to complete the manufacturing process.

With reference to FIG. 1, an improved work piece 10 is shown having afirst sheet metal blank 20 and a second sheet metal blank 30. The blanks20, 30 each have at least one joining edge 22, 32 each formed with aprecision sheared edge 25, 35, respectively. Prior to butt welding, theblanks 20, 30 are pressed flat onto a welding surface (not shown) withthe precision sheared edges 25, 35, pressed tightly together. As can beunderstood with reference to FIGS. 2 and 2a, when the edges 25, 35 areso positioned, they are ideally in facing contact with one another overthe entire length of the interface between them. However, under even themost controlled and the most tightly toleranced of manufacturingconditions, uninterrupted contact of the edges 25, 35 is unachievable,and some gaps 38, although very small, are experienced at the interfaceof the edges 25, 35. These gaps 38 are due to the normal manufacturingtolerances encountered with the manufacturing process and are alwaysexperienced during production. In the preferred embodiment, the gaps 38between precision sheared edges 25, 35 are preferably betweenapproximately zero and approximately 0.08 millimeters and morepreferably less than 0.04 millimeters.

These gaps 38 can cause problems with welded joints such as butt welds.This is because the gaps 38 can lead to less than optimum welds due tothe development of macroscopic and microscopic cracks and micropores,among other irregularities and anomalies, in the weldment between thejoining edges 22, 32. If not properly accounted for in the design,strength analysis, and manufacturing process, or if not otherwiseminimized during the manufacturing process, these types ofirregularities and anomalies can lead to increased numbers of rejectedwelded work pieces 10. Despite such anomalies and irregularities, thegaps 38 can be significantly minimized during the manufacturing processwhich, in turn, substantially reduces the number of rejected work pieces10. The gaps 38 are minimized by precision shearing the joining edges22, 32, to achieve the above gap dimensions, before welding. FIGS. 3, 3a, and 3 b schematically represent the welded interface or weldment 40.The preferred characteristics of the weldment are described below withrespect to the discussion of the laser weld inspection device of thepresent invention.

The preferred embodiment of a welded work piece produced in accordancewith the present invention includes blanks 20, 30 of substantiallysimilar or dissimilar thickness. For purposes of illustration but notlimitation, the thickness for each blank 20, 30 can range preferablyfrom between approximately 0.4 millimeters to approximately 2.0millimeters, and more preferably from between approximately 0.7millimeters to approximately 1.4 millimeters. In one embodiment of theinvention, one blank thickness is between approximately 0.50 millimetersand approximately 0.75 and the other blank thickness is betweenapproximately 1.25 millimeters and approximately 1.50 millimeters. As anexample of such dissimilar thickness, the first blank 20 can be selectedto have a thickness of approximately 0.7 millimeters while the secondblank 30 can be selected to have a thickness of approximately 1.4millimeters. Many various thickness arrangements of first and secondblanks 20, 30 are possible. The preceding example is particularlyeffective for use in manufacturing a welded work piece suitable forapplications where increased rigidity must be imparted to a portion ofthe work piece. This example is especially efficient in applicationswhere the added rigidity must be accomplished without a correspondingincrease in the part count or the part weight, as would occur ifstiffeners, pads, or other structural supports were added to the workpiece.

Although representative dimensions are set forth, they are presentedonly for purposes of demonstrating a particular embodiment of thepresent invention and not for purposes of limitation. One havingordinary skill in the art will understand that various types andthicknesses of steel, steel alloy, and other metal materials, arecontemplated for use with the present invention.

As a further illustrative example, the usefulness of the preferredembodiment is readily apparent in aeronautical or automotiveapplications. In aeronautical applications, structural rigidity must beaccomplished with minimum possible weight and part count to minimize theoverall aircraft weight and manufacturing cost. Similarly, in automotivemanufacturing, where millions of copies of the same part are fabricated,minimized weight and part count can translate into substantial savingsin material costs and manufacturing times. With reference to FIG. 4, arepresentative preferred embodiment of the improved welded work piece isshown as applied to the fabrication of a drawn or stamped body panel 50configured for use in the automotive vehicle manufacturing industry.First and second blanks 20′, 30′ are welded together along weld seam 40′after precision shearing the respective joining edges. The improvedwelded work piece is then stamped or drawn into the desired shape of anautomotive vehicle body panel.

System Disclosure

The present invention also provides a significant improvement overpreviously known welded work pieces and the system and method for theirmanufacture. With reference to FIG. 5, the invention includes anautomated welded work piece manufacturing system 100 configured torobotically retrieve a plurality of blanks, to form at least onerespective precision sheared edge on the blanks, to weld the blankstogether, to inspect the weldment, and to robotically output thesatisfactorily welded work pieces to an accepted station and theimproperly welded work pieces to a rejected station.

The blanks to be welded are fed to the automated manufacturing system100 by at least one of plurality of articulating arm feeder robots. Theautomated manufacturing system 100 includes one or more controlcomputers 105 configured to communicate with, monitor, and/or controlthe various subsystems and components of the system 100. With referenceto FIGS. 5 and 9, also included is at least one of a plurality ofrobotic stations that preferably include at least a first robotic feederstation 110 that incorporates a first articulating arm feeder robot 120that is capable of variable operation speeds and of 1, 2, or 3dimensional motion with articulation about substantially 2 tosubstantially 5 axes each ranging between approximately 5 toapproximately 360 degrees. Although not required for purposes of thepreferred embodiment, each robot may also incorporate a vertical andhorizontal telescoping capability for added flexibility. The first robot120 further includes a manipulator 125 configured to releasably capturea first sheet metal blank 130 of a plurality of blanks 135 for transportbetween at least two positions. Many types of suitable robots arecommercially available and include the Model SK-120 industrial robotavailable from Motoman, Inc., of West Carrolton, Ohio.

Preferably, the first robot 120 retrieves the blank 130 from at leastone of a first plurality of feeder pallets or skids 140 containing theplurality of palletized blanks 135. Typically, the first robot isconfigured to empty one skid at a time and then to begin removing blanksfrom the next available skid. The first robot 120 can be configured toretrieve a predetermined number of blanks 130 from the skid 140 beforeit begins to retrieve blanks 130 from the next available skid 140.Alternatively, the skids 140 themselves may be configured to detect alow quantity or empty skid. To accomplish this, each of the skids 140includes a quantity detector assembly 145 adapted to determine whetherthe quantity of remaining blanks 130 is low or zero, or both, by usingeither a light sensor, a weight detector, or a video system, or somecombination thereof. Upon determining a low or zero quantity, thedetector assembly 145 signals either the first robot 120 or any of thecontrol computers 105. In response, either the first robot 120 or any ofthe control computers 105 can take a selected skid 140 out of serviceand initiate retrieval of blanks 130 from the next available skid 140.For purposes of alerting supervisory personnel of the need to refill theempty skid 140, the detector assembly 145 can be adapted to alsogenerate a visual, audible, or electronic alarm or signal. In amodification to the preferred embodiment, the quantity detector assembly145 can be adapted for attachment to the manipulator 125 of the firstrobot 120 so that the detector assembly 145 detects low or empty skids140 when it attempts to capture and retrieve the next blank from theskid.

For safety purposes, the first robotic feeder station 110 issubstantially surrounded by a safety fence or partition 150 configuredwith light curtain assemblies or specially adapted doors, or both, todetect intrusions into the work area of the first robotic feeder station110. The partition 150 incorporates a plurality of spaced apart lightcurtain sensors 155 operative to signal an alarm when an intrusionoccurs. These types of sensors are commercially available from manyvendors including Scientific Technologies, Inc. of Fremont, Calif. Thealarm is selected to be either visual, acoustic, or electronic, or acombination thereof. The alarm, in turn, is configured to generate oneor more resulting alerts. First, the alarm can visually or audibly warnan individual intruder or supervisory personnel of the presence of anintrusion into the potentially dangerous area adjacent to the firstrobot 120. Also, the alarm can electronically signal the first robot 120or any of the control computers 105, or both, that an intrusion of thefirst robotic feeder station 110 has occurred. If an intruder hasentered the first station 110 work area, then either the first robot 120or one of the control computers 105, or both, can generate furtheralarms. The first robot 120 can also be configured to completely ceaseoperation to prevent injury to the intruder. Similarly, any of thecontrol computers 105 can be configured to stop the first robot 120 fromoperating, and can further stop the entire system 100 from operations sothe intruder can safely exit the first station 110.

Additionally, the light curtain partition 150 includes spaced apartlight curtain skid removal sensors 160 proximate to each of the feederskids 140 of palletized blanks 135. The removal sensors 160 areconfigured to operate in cooperation with the quantity detectorassemblies 145 and to communicate a skid removal alert signal to eitherthe robot 120 or any of the control computers 105 when an operatorapproaches and engages any of the feeder skids 140 for removal of theempty or low quantity skid 140 and replacement with a full skid 140.When a skid 140 has already been identified as empty or low, the removalsensor 160 can be adapted to generate the skid removal signal or toremain silent. Also, even if the detector assembly 145 has not generateda skid low or empty alert signal, the skid removal sensor 160 isconfigured similarly to the detector assembly 145 to alert the firstrobot 120 or any of the control computers 105 that blanks 130 must beretrieved from the next available skid 140. Thus, an operator can easilyremove and replace any skid 140 that is low or empty. When a skidremoval alert signal is generated, the first robot 120 is configured toretrieve blanks 130 only from one of the other skids 140 of theplurality. In this way, the system 100 can continue full speedoperations while empty or low skids are replaced with full skids.

As depicted in FIGS. 5 and 9, the system 100 may include a second robotfeeder station 170 configured with some or all of the capabilities ofthe first robotic feeder station 110 including, for example, a secondrobot 175. For purposes of illustration but not limitation, the secondstation 170 is spaced adjacent to or apart from the first station 110.It can include, for example, each or combinations of the components,assemblies, and capabilities of the first station 110. The secondstation 170 is configured to retrieve a second sheet metal blank 180from a plurality of palletized blanks 185 that are stored on a pluralityof feeder skids 190. As before, the skids 190 have some or all of theelements of the feeder skids 140. The blanks 180 may have a thicknesssimilar or dissimilar to the blanks 130.

The one or more robotic stations 120, 175 are located proximal to aprecision conveyer assembly 200 that incorporates a precision shearingmachine 210, as can be understood with reference to FIGS. 5, 8, and 9.The precision conveyor assembly 200 may be configured with asubstantially flat bed or a pre-shaped support jig 215 and plurality ofprecision sub-conveyors 220, 225 configured to precisely locate relativeto one another, a plurality of work piece blanks such as blanks 130,180. The precision conveyor 200 is adapted to releasably restrain thereceived blanks 130, 180 after they are received from the robotic feederstations 110, 170. The restraint mechanism may include a plurality orcombination of vacuum, magnetic, or clamping devices arranged on aconveyor bed 230 about the conveyer assembly 200 or sub-conveyers 220,225 to releasably capture the blanks 130, 180. After receipt and captureof the blanks, the conveyer assembly 200 or sub-conveyers 220, 225precisely position the blanks 130, 180 relative to each other and movethem into a machining or shearing position proximal to the precisionshearing machine 210. The conveyor assembly 200 or sub-conveyers 220,225 each include actuatable locator assemblies 228 arranged about theconveyer bed 215 that are operative to engage or push against one ormore of the exterior sides of the blanks 130, 180 to orient and positionthe blanks relative to each other and the shearing machine 210 with thejoining edges of the blanks 130, 180 arranged in a facing andsubstantially parallel relationship. The locator assemblies 228 arepreferably actuated with air-cylinders or any or a wide varietycommercially available industrial air, pneudraulic, and hydraulicsystems. Many suitable conveyors having such positioning assemblies areavailable from a number of commercial suppliers and a magnetic conveyorsuitable for use as the above configuration is available from VILMagnetic Conveyors of Chicago, Ill.

The preferred precision shearing machine 210 includes dual shear dies orblades and corresponding platens (not shown) configured tosimultaneously shear a portion of a joining edge from each of the blanks130, 180. Each of the dies and corresponding platens incorporateprecision machined outside corner edges that are precisely aligned witheach other to impart a precision sheared edge on each of the blanks 130,180. Each die and each platen can also be fabricated to include aplurality of precision machined edges so that the dies and platens maybe removed, reversed or rotated, and replaced when one of the edgesbecomes worn or out of tolerance. In this way, each die and platen maybe reused more than once before the outside corner edges of each die andplaten must be remachined to restore the precision toleranced edge.Accordingly, each die and each platen can preferably include fourprecision machined edges. Alternatively, at least two precision machinededges are achievable. Each edge is machined to impart a precisionsheared edge to each blank 130, 180 so that when positioned into anabutting relationship, the sheared edges are substantially in uniformcontact with each other with a minimized gap therebetween of betweenapproximately zero and 0.08 millimeters.

Preferably, between approximately 1 millimeter and approximately 10millimeters are removed from the blanks. More preferably, betweenapproximately 3 millimeters and approximately 5 millimeters are removed.Removal of this amount of material assures that enough material isremoved to eliminate possible edge defects in the raw stock material.Also, removal of at least this amount of material ensures that a cleanshear results with a minimized amount of possible tolerance anomalies.In turn, when the precision sheared edges are pressed together, theinterface between the edges will be in substantially uniform contactwith a correspondingly minimized gap therebetween. The use of dual sheardies and platens improves efficiency because shearing of both blanks130, 180 is accomplished in a single step. However, a single die orblade is a suitable alternative for lower throughput applications. Thepreferred precision shearing machine 210 also automatically removes thesheared scrap from the machine before the blanks are transferred fromthe machine. For purposes of illustration only, and not for limitation,a suitable hydraulically operated, dual die, precision shearing machineis available from VIL of Chicago, Ill.

After shearing the joining edges of the blanks, the conveyer assembly200 or sub-conveyers 220, 225 release and transfer the blanks 130, 180to an idle or queuing station 230 as can be seen with reference to FIGS.5 and 9. The queuing station 230 operates to temporarily store thesheared blanks before welding. In an alternative embodiment, not shown,the idle station 230 can be replaced with at least one transfer robothaving some or all of the capabilities of the first and second robots120, 175. By temporarily storing the sheared blanks 130, 180, anotherset of blanks may be retrieved, aligned, and sheared by the precisionshearing machine 210.

Laser Welder Disclosure

As illustrated in FIGS. 5 and 10, a second conveyor 240 slidablyrepositions the blanks 130, 180 and moves them from the idle station 230onto a welding bed 330 of a laser welding gantry 300. To protect workersand other nearby equipment from injury due to reflected laser energy orplasma, sputter, and other debris, the laser welding gantry 300 ispreferably enclosed. With reference also to FIGS. 5, 6 a, and 6 b, thegantry 300 incorporates a numerically controlled laser welder 350configured to move across the gantry 300 and incorporating a laser weldhead 355 and a laser weld inspection device 400. Although in someapplications a self-contained laser could be used, the preferredembodiment of the present invention includes a laser weld head 355 thatis powered by a remote laser unit 380 through a fiber optic cable 360contained in a cable support tray 390.

The laser welding gantry 300 incorporates an automated positionadjustment and orientation system having a plurality of pusher elements305 retractably arranged on the second conveyer 240 about the laser weldbed 330. The pusher elements 305 are generally retracted down into thesecond conveyer 240 until the blanks are moved onto the laser weld bed330. Once in place, the locator assemblies 305 are actuated and rise upto releasably engage the exterior edges of the blanks 130, 180, pushingthe blanks into alignment so the precision sheared edges are registeredsubstantially in parallel with each other and compressed into tightcontact so that any gap between the precision sheared edges isminimized. Such locator assemblies can be similar in design to thoseemployed by the precision conveyer 200. Once the edges are registeredand in contact, a clamping mechanism 310, spanning substantially acrossthe width of the gantry 300 above the welding bed 330, is deployed so aplurality of clamp members 315 clamp down on the blanks 130, 180 to holdthem in place against the bed 330 during welding.

The laser welder 350 is movably attached to the welding gantry 300 andis preferably numerically controlled by an appropriately programmedcomputer that can include any of the control computers 105. The welder350 is controlled to maintain a precise speed as it is moved across thegantry 300 during welding. The welder includes a laser weld head 355that is connected by a fiber optic cable 360 to a remote laser powerunit 380. With reference to FIGS. 2, 3 a, 3 b, 6 a, 6 b, 6 c, and 7, itcan be understood that the weld head 355 is configured to focus andproject a laser beam 370 incident to and focused upon the minimized gap38 between the precision sheared edges blanks 130, 180 to irradiate theregion around the precision sheared edges to weld them together byforming a weld bead seam 40, 40′.

Many types of lasers are commercially available for various weldingapplications. For purposes of the present invention, however, it ispreferable to use a single or dual cell (with corresponding single ordual optical fibers), solid, non-pulsed, continuous laser such as aneodymium doped, hard synthetic yttrium aluminum garnet laser (Nd-YAG).Preferably, the laser has output power rating of at least approximately2.5 to approximately 3.0 kilowatts, and is preferably capable ofgenerating a power output at the laser weld head 355 of at leastapproximately 2.3 to approximately 2.8 kilowatts, and more preferably alaser weld head 355 output of approximately 2.4 kilowatts. A suitableNd-YAG laser includes the Model LW-8 Laser Blank Welder available fromLumonics, Inc. of Livonia, Mich. Similarly powered gas and pulsed laserscan be used provided that they are capable of producing the specifiedpower ranges. Although a single cell, single fiber laser is representedby the figures, a dual cell laser will be equally effective and willincrease the throughput of the laser welder 350 accordingly.

A gas jet 385 is also part of the laser welder and the gas stream isdirected in the forward direction following the direction of the travelof the laser beam 370 and onto the region of the edges being irradiatedby the beam. The gas jet 385 produces a jet stream that reduces andideally eliminates gaseous contamination of the weld and to minimizeplasma shielding effects. The gas jet is preferably any of a number ofinert gases including, for example, argon, helium, or nitrogen, and canalso be directed against the underside of the weld region for additionalprotection of the weld. The forward direction of the resultant jetstream also “blows” the plasma cloud and other welding debris forwardand away from the laser weld head 355 and its associated and proximatecomponents including the inspection device discussed below.

With particular reference to FIGS. 6b and 6 c, it can be seen that thelaser beam 370 is focused to intersect the seam or interface 40 of theblanks and to irradiate their upper surface. The beam 370 projects at acompound angle to the vertical direction perpendicular to the surface ofthe blanks 130, 180. The compound angle includes “leading” and “leaning”components. The vertical direction is represented by the “Y” directionof the reference coordinate system labeled “A” in FIGS. 6b and 6 c. The“X” direction represents the forward direction of the incident laserbeam 370 across the gantry 300 during welding. With reference to FIG.6b, the laser beam 370 leading angle component is labeled “θ” (theta)and it is measured from the direction of the “Y” axis. Preferably, theleading angle, θ, is between approximately 5 degrees and 15 degrees,more preferably between 7and 12 degrees, and is most preferablyapproximately 10 degrees.

The leading angle serves several important functions. First, the leadingangle, θ, prevents reflection of incident laser energy back into thelaser weld head 355 and, in turn, into the laser unit. Next, leadingangle θ allows the laser weld head 355 to lag the point on the surfacewhere welding occurs. This protects the weld head 355 from contactingthe plasma cloud and weld spatter and debris during welding. Third,leading angle θ changes the shape of the laser beam spot that irradiatesthe weld seam region. Ordinarily, the weld beam spot would be a circleif the beam was perpendicular to the work piece surface. However, acircular weld spot creates a very high energy density that createswelding problems that are difficult to control by adjusting the speed oftravel of the laser beam 370. Thus, it has been found that by impartingan angle from the perpendicular to the incident direction of the laserbeam 370, the laser beam spot will achieve an elliptical shape on theirradiated surface with the major elliptical axis substantially parallelto the direction of travel of the laser beam spot or the X direction ofFIG. 6b. In turn, the elliptical shape reduces the energy density on theirradiated surface by spreading it over a larger area. The reducedeffective energy density of the laser beam spot allows better control ofthe welding process by variance, for example, of a single weldingparameter such as the speed of travel of the laser beam spot across theweld seam. Such techniques are described in a number of U.S. Patentsincluding, for example, U.S. Pat. No. 5,595,670 to Mumbo-Caristan whichis hereby incorporated by reference in its entirety.

With reference to FIG. 6c, the reference coordinate system A describesthe same Y direction as depicted in FIG. 6b. The “Z” direction points inthe lateral direction of the blanks 130, 180 (the Z direction isdirected up and out of the plane of FIG. 6b). In FIG. 6c, the Xdirection is directed up and out of the plane of the view. The leaningangle component of the compound laser beam angle is labeled “γ” (gamma).Preferably, angle γ is between approximately 1 and approximately 10degrees, more preferably between 3 and 7 degrees, and is most preferablyapproximately 5 degrees. The leaning angle γ serves to further impart anelliptical shape to the laser beam spot with the major elliptical axisdue to angle γ substantially perpendicular to the direction of beam spottravel and the X direction of FIG. 6b. When welding blanks ofsubstantially similar thickness, the beam spot is focused and positionedto irradiate substantially equal regions of the blanks on both sides ofthe weld seam. However, when welding blanks of substantially dissimilarthickness, the leaning angle γ is configured to precisely positionapproximately between 15 percent and 30 percent, and more preferablyapproximately 25 percent of the cross-sectional area of the ellipticallaser beam spot upon the protruding vertical face of the thicker blank(see reference numeral 35 of FIG. 2). It will be understood that theremaining portion of the beam spot will irradiate the thinner blank.

With these desired leading and leaning angles, the preferred speed oftravel of the laser beam spot across the blanks, as controlled by thespeed of the laser welder 350 that creates the optimum weld bead seam ispreferably between approximately 4 and approximately 10 meters perminute, and more preferably approximately 7 meters per minute. Thesewelding parameters have been used to create a welded work piece whereinthe welded seam is at least 30 inches in length and has a tensile, pullstrength exceeding approximately 9,000 pounds per square inch.

These angles and speeds were empirically derived and are based uponextensive trial and error experimentation because no data existed as tohow the Nd-YAG laser would perform in welding dissimilar thicknessmaterials at speeds greater than that possible with the prior art gas,pulsed, and CO₂ lasers. The preceding parameters have thus beendiscovered to significantly minimize laser weld anomalies, such asburn-through, cracking, and pores.

Inspection System Disclosure

The laser welding system 100 also preferably incorporates a laser weldinspection and quality control device 440, as represented in FIGS. 6aand 6 b, which is mounted to cooperate with the laser welder assembly350 of the gantry 300. In FIGS. 6a and 6 b, the laser welding inspectiondevice 400 is shown mounted to the gantry 300 to move along with thelaser welder 350 during the welding operation.

As the laser weld head 355 projects the laser beam 370 to irradiate theseam 40 between the work pieces 130, 180, a molten weld pool 402 isgenerated at the focal point 404 of the laser beam 370. As the laserbeam 370 and weld pool 402 traverse the seam 40, a weld bead is created.The laser weld inspection device 400 utilizes an image capturing device,namely a visual sensor 410, such as a CCD (Charge Coupled Device), or ahigh shutter speed video camera. For purposes of illustration, and notlimitation, an example of a visual sensor 410 is the model MVS-5 camerafrom Modular Vision Systems of Montreal, Canada. Preferably, the visualsensor 410 is mounted rearward of the laser weld head 355 using astructure such as a camera mounting bracket 420, although in analternative embodiment of the present invention, the visual sensor maybe self-propelled and have its own support structure. The visual sensor410 is focused on the welding path, at a predetermined distance 425behind the laser's current focal point 404. The distance 425 between thefocal point of the laser 404 and the focal point of the visual sensor430, is selected so that the images captured by the visual sensor 410will reflect a fully solidified weld bead. In the preferred embodimentof the invention, the distance 425 is between approximately 75millimeters and approximately 200 millimeters, and more preferablybetween approximately 100 millimeters and approximately 200 millimeters.Even more preferably, the distance 425 is about 150 millimeters. Thevisual sensor 410 is also mounted at a specific angle “φ” (phi),preferably between approximately 5 and approximately 10 degrees towardthe direction of travel, labeled as the X direction in the figures. Inthe preferred embodiment of the invention, the visual sensor 410 has afield of view of approximately 5 millimeters by approximately 5millimeters, although the field of view may be altered based on the sizeof the weld to be inspected.

The visual sensor 410 is configured to capture images of the weld beadat predetermined time intervals based on considerations such as thelinear velocity of the laser weld head 355 and the particular featuresof the weld bead to be inspected. In one preferred embodiment of thepresent invention, the visual sensor 410 captures approximately oneimage per every 4 millimeters of travel while moving at a linearvelocity of approximately 6 meters per minute.

A representative cross-sectional view of a weld to be inspected is shownin FIG. 3a. The blanks 130, 180 are selected to be of dissimilarthickness and are fabricated from a material such as, for example, steelsheet metal blanks. The blanks, are joined through a seam whose lengthis normal to the surface of the paper. The blanks 130, 180 are joined bywelding using the laser welder 350. The intense heat of the laser beam370 creates a melt zone 440 as it contacts the seam 40 between theblanks. As this melt zone cools, the weld bead 445, 450 forms on boththe top and bottom surfaces of the welded work piece.

FIG. 7 describes a representative comparison procedure that is includedin the system software of the present invention. As the laser weld head355 follows the seam, the visual sensor 410 trails directly behind,viewing an image of the fully formed weld bead 445 at predefinedintervals. The images captured by the visual sensor are electronicallycommunicated to a selected computer, such as one of the controlcomputers 105, that incorporates an image processor having imageprocessing hardware or software, or both. The image processor firstanalyzes the image to determine the edges of the weld bead. The imageprocessor then measures the image in several preselected dimensionalareas, which will be described in detail below. The image is firstmeasured for bead width A and top mismatch B, (FIG. 3a). After beadwidth A and top mismatch B are calculated, the image processor measuresthe image for top concavity C and top convexity D. The selectedcomputer, or any of the other control computers 105, or both, alsoinclude a distinction device that incorporates an image coprocessorhaving hardware or software components, or both, and in electroniccommunication with the image processor. The distinction devicecooperates with the image processor to compare the values of bead widthA, top mismatch B, top concavity C, and top convexity D withcorresponding reference images or values, or both, that represent thevalues of acceptable weld parameters and dimensions.

Once the comparison of each selected dimensional area is complete, thedistinction device determines the quality of the weld and whether thewelded work piece should be accepted or rejected. If it is determinedthat the selected characteristics of the weld bead image are within thelimits of the predetermined, acceptable weld parameters and dimensions,a signal is generated classifying the weld as acceptable. If it isdetermined that the image is outside the predetermined, acceptable weldparameters and dimensions, a signal is generated classifying the weld asrejected. The signal may also be used to initiate the next appropriatemachine process step to be performed on the welded part. For example,the signal may be sent to the removal station 510 described below andthe articulating arm robot 520 for removal to an accepted work pieceskid 530 or a rejected work piece skid 540.

As described in the procedure of FIG. 7, in a preferred embodiment ofthe invention, the captured images and the reference images areanalogized in four specific dimensional areas Referring again to FIG.3a, these dimensional areas are depicted as bead width A, top mismatchB, top concavity C, and top convexity D.

Bead width A is the distance between the two limit points defining theedges of the weld bead 445, measured along an axis perpendicular to thelength of the seam on the top surface of the work pieces 130, 180.

As shown in FIG. 3a, the work pieces 130, 180 are preferably aligned tohave each of their bottom surfaces in the same plane. If the work piecesare of substantially dissimilar thickness, then top mismatch B willexist as the difference in height between the top surface of one blank130, and the top surface of the other blank 180. Although top mismatch Bis depicted in the preferred embodiment of FIG. 3a, the work pieces mayalso be of substantially equivalent thickness, with both their top andbottom surfaces lying in the same plane. In this case, mismatch betweenthe adjoining work piece surfaces would be negligible.

The images are also compared for top concavity C, which is the maximumdepth to which the weld bead 445 has sunken, measured from the topsurface of one of the blanks or the thinner blank 130, if they are ofdissimilar thickness. The reference surface for purposes of the topconcavity C measurement may change based upon the alignment andthickness of the work piece blanks 130, 180.

The fourth dimensional area selected for purposes of comparison is topconvexity D. Top convexity D is the maximum height of the weld bead 445,measured from the top surface of the blanks or the top surface of thethicker blank 180 if blanks of dissimilar thickness are used. Like topconcavity C, the reference surface for purposes of the top convexity Dmeasurement may change based upon the alignment and thickness of thework pieces 130, 180.

In an embodiment denoted in FIG. 3a, all images of the weld bead 445 aregenerated by the visual sensor 410 from above the work pieces. However,it should be understood that it is also possible in another embodimentof the invention, to utilize an additional visual sensor for viewing theportion of the weld bead 450 formed along the bottom surface of the workpieces 130, 180. Additional dimensional comparison areas may also beincluded in the weld bead analysis. These additional comparison areas,as denoted in FIG. 3a, may include root width E, bottom concavity F, andbottom convexity G. Further, an additional visual sensor may beincorporated for use in a dual-cell laser configuration of the presentinvention so that more than one segment of the weld bead may beinspected in cooperation with each of the dual laser weld heads. Rootwidth E is the distance between the two limit points defining the edgesof the weld bead 450, taken along an axis perpendicular to the length ofthe seam on the bottom surface of the work piece.

As illustrated in FIG. 3b, the blanks 130, 180 may be aligned so neithertheir respective top nor bottom surfaces lie in the same plane. In thiscircumstance, bottom mismatch H will occur as the difference in heightbetween the bottom surface of one blank, and the bottom surface of theother blank. Bottom mismatch may also be selected as a dimensionalcomparison area.

Referring again to FIG. 3a, bottom concavity F is shown as the maximumdepth of the weld bead 450 below the bottom surface of the work pieces130, 180. The maximum height of the weld bead 450 as measured from thebottom surface of the work pieces may also be checked. This measurementis defined as bottom convexity G.

The selected dimensional comparison steps are described above in anexemplary sequence representative of the preferred embodiment of thepresent invention. However, any sequence of the above steps is equallysatisfactory and the preceding description is presented for purposes ofillustration but not limitation. Moreover, the exemplary proceduresetting forth the comparison and analysis steps is not limited to anyparticular number or combination of dimensional areas described above.Additional inspection steps may be added, and existing steps may beremoved without departing from the scope of the invention.

New reference images may be created that adopt existing dimensionalcomparison areas, create new areas, or utilize combinations of both. Areference image may have adjustable tolerance zones which can be set foreach area of dimensional comparison. In this manner, distinct referenceimages can exist for use under particular conditions.

A visual display monitor, such as is well known, may be connected to theimage processing board or any of the control computers 105, or both, todisplay the weld bead image captured by the visual sensor 410. Anadditional monitor may be connected to display, for example, thereference image or dimensional comparison area tolerance zones usinggraphic overlays of the predetermined parameters. The system may alsoemploy a communication board to send signals to other equipment, suchas, for example, any of the control computers 105, as dictated by theresults of the weld bead analysis and for purposes of archiving capturedimages for future analyses and comparisons.

In the present invention, a clear image of the weld bead is critical.Therefore, it is necessary to safeguard the visual sensor 410 fromcontamination. Although the visual sensor 410 is maintained at apreselected distance 425 (FIG. 6b) rearward from the laser weld head355, the visual sensor 410 is sufficiently proximate the weld pool 402to be affected by plasma, weld spatter, and other debris. Plasma, smokeand particles of liquid metal (spatter) that are emitted from the weldpool 402 during the welding process, may migrate to, and damage thevisual sensor 410. Therefore, a means for preventing such damage ispreferably utilized. In one preferred embodiment of the invention, acompressed air stream 485 is employed to pass across, and deflect anyerrant debris away from the visual sensor. Other methods such as the gasjet 385 used with the laser weld head 355, filters or vacuum means, forexample, may be applied to perform an equivalent function.

With reference to FIGS. 5 and 11, an exit conveyer station 500 isdepicted as part of the automated welding system 100. The station 500includes an exit conveyor 505 that cooperates with the second conveyor240 to transfer the welded work piece from the laser welding bed 330 toa removal station 510. The removal station can include anotherarticulating arm robot 520 that is similar in design to and can includeany or all of the features of the robots 120, 175 already described.Depending on whether the welded work piece has been accepted or rejectedduring the inspection of the laser weld, the removal robot 520 willremove the work piece from the exit conveyer 505 and put it onto one ofa plurality of accepted skids 530 or on a reject skid 540. Since thequantity of rejected parts is likely to be very small and since it maybe desirable to immediately remove and inspect any rejected work pieces,it may not be necessary to put the rejected pieces on a skid. In such acase, 540 may be replaced by a gravity roller conveyor or other meansfor removing the work piece from the automated welding system 100. Forworker safety, the exit conveyor station 500 is configured similar tothe feeder station 110 and is surrounded with a safety fence orpartition 545 configured with light curtain assemblies or speciallyadapted doors, or both, to detect intrusions into the work area of theexit station 500. Additionally, the accepted skids or the rejectedskids, or both, are surrounded by light curtains 555 having the samecapabilities described with respect to the feeder station 110.

Industrial Applicability

From the foregoing, it can be appreciated that the present inventionfulfills a real but heretofore unmet need for a structurally improvedwelded work piece that is less expensive to manufacture, includes fewerparts, and is lighter in weight. The present invention also fulfills theneed for a method for manufacturing such a welded work piece thatovercomes the undesirable features, deficiencies, and shortcomings ofpresently available welded work pieces and methods for theirmanufacture. The invention fulfills these needs of the automotiveindustry through the novel design of a welding gantry that comprises alaser beam aimed at a compound angle, to irradiate the pieces to bewelded. The welding gantry may also comprise an inspection device thattravels with the laser welder during the welding operation. Theinspection device captures images of the weld bead and transmits thoseimages to an image processing board. Various weld bead parameters arethen compared to reference values by a distinction device. If the weldbead is within tolerance on all parameters, the work piece is consideredaccepted and moved to an accepted work piece skid. If the weld bead isnot within tolerance on all parameters, the work piece is consideredrejected and moved to a rejected work piece skid. The welding gantry mayalso comprise protection means for the welding head and/or theinspection device, such as gas streams.

The invention also fulfills the needs of the automotive industry forimproved work pieces through the use of an automated system thatcomprises robots for the transport of sheet metal blanks to a conveyorsystem, a conveyor system, a precision shearing device, a laser weldinggantry, and robots for the transport of welded work pieces from theconveyor.

Each of the described embodiments and variations, as well as otherobvious yet undescribed embodiments of the invention, and equivalentsthereof, may be used either alone or in combination with each of theother embodiments. While particular preferred embodiments of theinvention have been illustrated and described, various modifications andcombinations can be made without departing from the spirit and scope ofthe invention, and all such modifications, combinations, and equivalentsare intended to be covered and claimed.

What is claimed is:
 1. A welded work piece comprising: a first blank ofsteel sheet stock having a pair of exterior surfaces with a firstthickness of between approximately 0.50 and 0.75 millimeters and havingat least one first precision sheared edge; a second blank of steel sheetstock having a pair of exterior surfaces with a second thicknessdifferent than the first thickness of between approximately 1.25 and1.50 millimeters and having at least one second precision sheared edge;a laser welded seam permanently joining the respective first and secondprecision sheared edges; wherein the respective first and secondprecision sheared edges of the respective first and second blanks arealigned to form a minimized gap therebetween of between approximatelyzero and 0.8 millimeters before being welded; and wherein the laserwelded seam is formed with a beam from a continuous wave Nd-YAG laser,the beam being at a compound angle to the minimized gap and having aleading angle θ of between approximately 5 and 15 degrees and a leaningangle γ of between approximately 1 and 10 degrees; and wherein the beamis focused substantially into an elliptical shaped spot about theminimized gap and approximately 70 to 85 percent of the cross-sectionalarea of the beam is incident on the first blank; whereby the welded seamhas a tensile strength exceeding approximately 9,000 pounds per squareinch.
 2. The welded work piece according to claim 1 wherein theminimized gap is approximately 0.04 millimeters.
 3. The welded workpiece according to claim 1 wherein the first blank thickness isapproximately 0.7 millimeters and the second blank thickness isapproximately 1.4 millimeters.
 4. The welded work piece according toclaim 1 wherein the welded seam is at least approximately 30 inches. 5.The welded work piece according to claim 1 wherein one of the respectiveexterior surfaces of each of the first and second blanks are coplanar.6. The welded work piece according to claim 1 wherein neither of therespective exterior surfaces of the first and second blanks arecoplanar.